The long-term objective is to understand the factors involved in oligo- dendrocyte development and myelination,. This information is pivotal to understanding not only dysmyelinating diseases such as Pelizaeus- Merzbacher disease, but also demyelinating diseases such as Multiple Sclerosis. The development of therapeutic approaches to such diseases requires detailed knowledge of the processes and factors involved in oligodendrocyte development. This laboratory is currently undertaking studies on the function of myelin proteolipid proteins in the initial steps of myelination. The focus of the proposed work is to further examine the role played by the proteolipid proteins in oligodendrocyte development. The specific aims are as follows. 1) Investigation of the expression of all isoforms of proteolipid protein expressed during embryonic and early postnatal development of wild-type and PLP mutant mice. One part of this study, using RT-PCR to document the expression of the different isoforms, will provide a more complete picture of the changes in expression of the isoforms of proteolipid during development, particularly before myelination begins, and therefore possibly illuminate other functions of the isoforms. The effect of a mutation in the PLP gene on its expression at different developmental stages will also be examined. The expression of new isoforms will be examined at the mRNA level by RNAse protection assay and RT-PCR. The new isoform will then be cloned and sequenced. Its function in oligodendrocyte development will be investigated in the transgenic mouse model currently being used to examine the function of the known proteolipid isoforms, by analyzing jimpy mice expressing the new isoform. 2) Development of a series of tissue-culture experiments to investigate the signals involved in the maturation of the oligodendrocyte and the sources of those signals. Brain cell cultures from PLP/DM20 transgenic mice will be used for investigating the role that PLP and DM20 play in the signal pathway.